1. Field of the Invention
This invention relates to a new ignition source for internal combustion engines, utilizing a radio frequency (RF) coaxial cavity resonator to produce a non-propelled plasma.
2. Description of the Related Art
Most prior art ignition sources attempt to ignite and completely burn a combustible fuel for maximum energy output and to minimize unwanted emissions i.e., pollutants. With regards to internal combustion engines, placement and/or volume of ignition energy are factors studied by industry to optimize engine performance. Methods of increasing the ignition energy volume fall into two categories: (a) changing the spark characteristics of spark ignition systems and (b) the use of plasma. Heretofore, plasma ignition sources have propelled the plasma entity at high velocities into the combustion chambers. This type of plasma ignition requires the consumption off large amounts of power, thus rendering these devices impracticable for automotive applications.
It is also known to generate a plasma using radio frequency power in a coaxial cavity resonator having an electrical length one-quarter of the radio frequency wavelength. The coaxial resonator is formed between two coaxial conductors which are shorted at the input end and electrically open at the output end. In this way, the input voltage is resonantly amplified to produce a plasma at the open end of the resonator.
Automotive internal combustion engines today burn air/fuel ratios between about 14:1 and 19:1, the latter being leaner. It is generally known by those skilled in the art of internal combustion engines that automotive engine fuel economy improves with leaner air/fuel ratios. Generally, the lean limiting value of air/fuel ratio is governed by vehicle drivability, which is in turn related to the consistency and smoothness of the combustion process. One way of improving automotive engine fuel economy is to provide a means for obtaining consistent and smooth combustion at air/fuel ratios which are leaner than possible with present ignition systems.
Significant improvement of standard spark ignitions cannot be attained because they ignite only a localized region of the combustion chamber, making ignition of very lean air-to-fuel mixtures difficult, or some stratified charge mixtures. This leaves plasma ignition, which heretofore has required large amounts of source power.
The prior art devices are either ineffective or use excessive amounts of power in order to burn sufficiently lean air/fuel mixtures. It is therefore an object of the invention to provide an apparatus for burning lean air-to-fuel mixtures greater than 19:1.
Another object off the invention is to provide an apparatus which requires considerably less power than existing plasma ignition systems.
A still further object is to provide an apparatus which is adaptable for use with existing internal combustion engines.